Hong Kong police early Monday started removing street barricades at sites where pro-democracy demonstrators have been holding more than two weeks of rallies, paralysing parts of the Chinese financial hub.

Police had started moving in to clear barriers at the edges of the main protest site in Admiralty, catching some demonstrators unawares after their numbers had dwindled overnight, AFP correspondents saw.

But protesters, some of whom had been sleeping in tents, remained at the site and the police said they were intent on clearing blockages to traffic rather than ending the protests outright, as morning commuters weaved around the opposing lines on foot.

"Police urge protesters to listen to the advice of the police, not to obstruct the police action, to remove obstacles blocking the roads as soon as possible, and to leave the scene in a peaceful and orderly manner," a police statement said.

The message was relayed on-site via megaphones. The police were dressed in high-visibility jackets but not wearing riot gear.

At least two dozen police vans were parked close to Admiralty, in Central, and police were also gathering at a secondary site in Mongkok.

There was a heated stand-off Sunday as a pro-government group marched on Mongkok - a flashpoint district which has seen ugly scuffles - with police intervening to keep them apart from the rival activists.

Some demonstrators in Admiralty early on Monday wielded umbrellas, which have become emblematic of the Hong Kong movement, to guard against any police pepper spray.

The demonstrators are calling for Beijing to grant full democracy to the former British colony and have brought parts of Hong Kong to a standstill over the last fortnight, prompting clashes with elements who oppose the blockades and widespread disruption.

Despite repeated orders to disperse, the rallies have taken on an air of permanence, with tents, portable showers and lecture venues - drawing thousands of people in recent evenings.

On Sunday, the city's embattled leader Leung Chun-ying said the protesters had "almost zero chance" of changing Beijing's stance and securing free elections.

After police were criticised for unleashing tear gas on the rallies in late September, Leung said that if the government had to clear the protests sites, police would use a "minimum amount of force".

China announced in August that while Hong Kongers will be able to vote for Leung's successor in 2017, only two or three vetted candidates will be allowed to stand - an arrangement the protesters dismiss as "fake democracy".

Students and pro-democracy campaigners have taken to the streets - sometimes in their tens of thousands - since last month to call for Beijing to change its position and allow unfettered elections and to demand Leung's resignation.

But Leung said Sunday: "In achieving universal suffrage in 2017, if the prerequisite is to put down the Basic Law and the decision made by the National People's Congress Standing Committee, I believe we all know that the chance is almost zero."

Crunch talks between student leaders and city officials collapsed last week, deepening the crisis in the semi-autonomous city as protesters vowed to dig in for the long haul.